1. Field of the Invention
The present invention relates generally to components and structures for wheelchairs. The present invention relates more specifically to mechanisms for retaining, supporting and tilting the seat platform of a wheelchair.
2. Description of the Related Art
It is desirable in many uses of a wheelchair to be able to move the seat platform of the chair to a reclining position. Efforts to achieve this capability have frequently failed to provide both a durable tilting framework and a low profile structure. Effective mechanisms typically have excessive structural requirements while low profile systems typically fail to operate very effectively.
It would be desirable to have a low profile seat tilting mechanism that operated smoothly and efficiently without the need for excessive power motor requirements. It would be desirable if such a low profile seat tilting mechanism could move the seat platform of the wheelchair through at least sixty (60) degrees of effective rotation or tilt. It would be desirable if such a mechanism could be implemented in a minimal amount of space below or within the seat platform of the wheelchair. Finally it would be desirable if such a tilt system provided stability to the seat platform throughout the range of motion possible.
It is therefore an object of the present invention to provide a tilt mechanism for a wheelchair seat platform that is both durable and low in profile.
It is an object of the present invention to provide a tilt seat mechanism for a wheelchair that provides a stabile range of motion of at least sixty (60) degrees from the horizontal to the inclined.
It is a further object of the present invention to provide a tilt seat mechanism for a wheelchair that incorporates a linkage system that minimizes the motorized power required to effect tilting movement of the seat platform.
It is a further object of the present invention to provide a tilt seat mechanism for a wheelchair that is rugged and durable in the face of repeated use and yet does not require excessively heavy linkage members and frame supports.
In fulfillment of these and other objectives the present invention provides an improved tilt seat mechanism for a wheelchair that is structurally durable, operationally effective, and yet low in profile, adding very little to the overall framework of the chair platform. The mechanism structure includes a base frame and a seat platform frame that are nested and parallel in a first position and separated and at an angle of sixty (60) degrees or more in a second position. The seat platform component is rotated about a pivot point on and with respect to the base frame, by an electrically driven jack-screw with a unique linkage between the frame components. The linkage comprises a movable cross bar connected to the end of the jack-screw as well as a pair of tee-head connecting links that move with the crossbar. The ends of the cross bar move in channels on the base frame and pivotally connect to the tee-head connecting links. The connecting links are each pivotally attached to a transverse lever bracket fixed on the seat platform frame. As the jack-screw turns it moves the cross bar and connecting links forward or out from a xe2x80x9cclosedxe2x80x9d position. Due to the placement of the pivot point for the seat platform frame, the movement of the connecting links outward pulls on the lever bracket of the platform frame and rotates the seat platform frame around the pivot point. This rotation results in the lifting of the seat platform to a reclining position with respect to the typically horizontal base frame.